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The present invention relates to a method and apparatus for providing an indication of the presence of an object within a pinch zone located in the path of an automated closure device such as a powered window, powered sunroof, powered door or hatch using an optical sensor, and more particularly to the use of an optical sensor that incorporates a synchronous detection amplifier to selectively amplify the desired light signal in the presence of ambient light and electronic noise.
Closures for apertures such as vehicle windows, sunroofs and sliding doors are now commonly motor driven. As a convenience to an operator or passenger of a vehicle, power windows are frequently provided with control features for the automatic closing and opening of an aperture following a simple, short command from the operator or passenger. Alternatively, automatic closing and opening of an aperture may be in response to an input from a separate device, such as a rain or temperature sensor. For instance, a driver""s side window may be commanded to rise from any lowered position to a completely closed position simply by momentarily elevating a portion of a window control switch, then releasing the switch. This is sometimes referred to as an xe2x80x9cexpress closexe2x80x9d feature. This feature is also commonly provided in conjunction with vehicle sunroofs. Auto manufacturers may also provide these features in conjunction with power doors, hatches or the like. Such automated aperture closing features may also be utilized in various other home or industrial settings.
In addition to providing added convenience, however, such features introduce a previously un-encountered safety hazard. Body parts or inanimate objects may be present within an opening when a command is given to automatically close the window or door. For example, an automatic window closing feature may be activated due to rain impinging on an interconnected rain sensor while a pet in the vehicle has its head outside the window. A further example includes a child who has placed its head through a window or sunroof that is activated to close by the driver, another passenger or accidentally by the child.
In order to avoid potentially tragic accidents or property damage involving intervening objects entrapped by power windows or sunroofs, systems have been developed which detect the circumstance in which a window has been commanded to express close but closure has not occurred within a given period of time. As an example, a system may monitor the time it takes for a window to reach a closed state. If a temporal threshold is exceeded, the window is automatically lowered. Another system monitors the electrical current drain attributed to the motor driving the window. If it exceeds a predetermined threshold at an inappropriate time during the closing operation, the window is again lowered.
The problem with such safety systems is that an intervening object must first be entrapped and subject to the closing force of the window or other closure device for a discrete period of time before the safety mechanism lowers the window or reverses the sunroof or other closure device. Personal injury or damage to property may still occur in such systems. In addition, if a mechanical failure in the window driving system occurs or if a fuse is blown, the person or object may remain entrapped.
Non-contacting object detection systems are known which detect the presence of an intervening object within an open area. Such systems include, for example, security systems and garage door safety interlocks, to detect interruption of a light beam across an opening. Other systems are used with automotive apertures having motorized closure members such as windows, sunroofs, and sliding doors, to detect an intervening object proximate or extending through the respective aperture. Undesired operation of an aperture closure member is therefore prevented when an intervening object such as a finger or arm is extended through the opening during closure; the closure member is not required to come into contact with the intervening object for the object to be detected.
Such object detection systems typically measure the magnitude of a reflected signal to determine the presence or non-presence of an intervening object. A photo-emitter emits a light beam which an optical system directs across the opening that is being monitored. An uninterrupted opening may result in the reflection of at least a some portion of the emitted beam from the opposing side of the aperture. A photo-receiver disposed in an appropriate location receives the reflected light beam and generates an output signal indicative of the intensity of the reflected beam. Reflection from the opposing side ordinarily results in a reflected signal of a well-defined intensity being returned to the receiver. Alternatively the emitted beam may be directed so that it may graze or not strike an opposing member in which case little or no light energy may be returned in the absence of an object in the opening. An intervening object located in the path of the light beam changes the intensity of the reflected light beam, a condition reflected in the detector output signal. The detector output signal with an object in the opening being monitored will thus differ from the detector output signal in the absence of an object. Depending upon the reflectivity of the intervening object and the reflectance characteristics of the aperture environment, the detector output signal will be greater or less than the nominal output signal from the detector.
These optical systems, however, are vulnerable to interference by ambient light such as sunlight as well as fluorescent and incandescent overhead illumination. Prior art solutions have included the use of synchronous detectors and xe2x80x9cjudgment circuitsxe2x80x9d consisting of a number of logic circuits coupled together. These judgment circuits however, are still susceptible to interfering sunlight. In addition, these judgment circuits typically include several steps each of which contains several digital logic circuits. The large number of parts associated with the judgment circuits can increase both the power that is consumed and dissipated as heat, and also can increase the cost associated with the object detection circuitry.
It would therefore be desirable to provide an apparatus and method for detecting the presence of an object by measuring a change in a light signal that is received in the presence of ambient light, and which can be calibrated or initialized in such a way so as to cancel the portion of the signal that is not associated with an obstacle. Preferably, such an apparatus provides enhanced accuracy by reducing the effect of the interfering ambient light while using fewer parts and consuming less power than then prior art.
A method and apparatus are disclosed for sensing an object by an optical sensor that utilizes synchronous detection and an integrator for separating a desired optical signal from ambient light and electronic noise as well as a means for canceling modulated energy from features of the environment not associated with an object in the opening.
In one embodiment, the system includes a modulator driving a photo-emitter and a switched amplifier with first and second modulation signals respectively. A photodetector receives a portion of light reflected from the pinch zone and/or an object therein and provides an optical detector signal to the switched amplifier.
The switched amplifier has a first input coupled to the optical detector signal and a second input connected to a reference voltage. This amplifier alternately switches between two phases thus providing a first gain corresponding to the active state of the photo-emitter and a second gain of opposite polarity corresponding to the inactive state of the photo-emitter. The switched amplifier provides an output signal that includes a first voltage that results from the difference between the amplified optical detector signal at the first input and the reference signal at the second input multiplied by the first gain during the active phase followed by second voltage that results from the difference between detector output signal and the reference signal multiplied by said second gain during the inactive phase. The first and second gains and the duration of the active and inactive phases of the measurement period are selected in such a way that the gain of said switched amplifier has an average value of zero when no optical signal is present when averaged over a predetermined measurement period which will include at least one pair of active and inactive phases and may include many such pairs.
The obstacle detection system further includes a means to electronically integrate the difference between output of the switched amplifier and an adjustable reference voltage for a predetermined measurement time. The integrator is configured and arranged to integrate the output signal of the switched amplifier over at least one active phase and inactive phase, and to provide an integrator output signal. A detector receives the integrator output signal and is configured and arranged to provide indicia of the presence or absence of an object within said pinch zone. In a preferred embodiment the reference voltage input to the integrator is selected so that the output voltage changes significantly only when an object is present in the monitored opening. A detector element monitors the integrator output signal and is configured and arranged to provide indicia of the presence or absence of an object within said pinch zone.